Introduction to cyclic GMP

As commented in previous pages, cyclic GMP is an important second messenger. Although it is distributed throughout the entire organism, cyclic GMP has crucial roles in brain, cardiovascular system and sensory organs (e.g. in light detection in retinal cells). In fact, living cells has been using cyclic GMP since the ancient times; this compound and its synthetic enzyme (guanylyl cyclase) have been detected throughout the animal kingdom, plants and even in bacteria.

The molecule

Guanosine 3',5'-(cyclic)phosphate (ussually abreviated as cyclic GMP or cGMP). For additional information about nomenclature of this type of molecules read the recommendations published by IUPAC-IUB Commission on Biochemical Nomenclature (CBN).

Cyclic GMP is chemically very similar to cyclic AMP. Cyclic AMP was the first molecule recognized as second messenger and its mechanisms of synthesis are known since decades. On the other hand, although cyclic GMP was also discovered very early (it was discovered in urine in 1963) and considered a second messenger since 1970, the regulation of its synthesis has remained a mystery until recently. The question has been solved by the discoveries of nitric oxide and natriuretic peptides.

The synthetic reaction

This enzyme, GTP diphosphate-lyase (cyclizing) [EC 4.6.1.2, see IUBMB Enzyme Nomenclature] is commonly denominated guanylyl cyclase, guanylate cyclase or guanyl cyclase and catalyzed the reaction GTP = 3',5'-cyclic GMP + diphosphate.